This invention relates to a pedal mechanism. The invention is particularly, but not exclusively, intended for use in a motor vehicle, for controlling a function of the vehicle. In particular, the pedal may be an accelerator pedal.
Although in this specification the invention is described in terms of a motor vehicle accelerator pedal, it will be appreciated that the invention may have other applications.
Accelerator pedals can be formed in one or more parts and are conventionally mounted in a floor assembly of the driver cell of a motor vehicle. The connection between an accelerator pedal and a throttle plate of a throttle mechanism is often made using a Bowden cable. The throttle plate is opened by the driver""s foot pressure on the accelerator pedal. One or two resetting springs are provided to draw the accelerator pedal and thus the throttle plate back to an idling position when the driver""s foot is lifted. In this way a link is provided between the pedal and throttle plate position on the one hand and a change in the engine speed on the other hand.
Due to the greater sophistication of new internal combustion engines, there is an increasing need to supply electronic engine systems with an electronic signal representing accelerator position. It is known to cause pedal movement to be converted into an electronic engine management signal. This is often referred to as xe2x80x98drive-by-wirexe2x80x99. However in order to produce the correct xe2x80x98feelxe2x80x99 which the driver is used to experience through the foot when driving a car with a Bowden cable linkage, it is necessary to produce, in a drive-by-wire system, a resistance to pedal movement which simulates the resistance and the same driving conditions which would have been produced using a cable linkage system.
Pedal mechanisms are known wherein the friction force is produced by means of separate pretensioned friction elements (e.g. DE 3 411 456 C2). Arrangements of this kind are complicated in construction and limiting for the size of the friction force. It is also important that if one spring breaks then a satisfactory and safe resetting must be possible. The safe resetting in the event of a spring breaking is an absolute necessity for reasons of product liability and is a legal requirement in the USA through safety standard FMVSS124.
There are already several proposals (e.g. DE 3 411 393 A1; EP A 0 092 640; WO A 89/07706; WO A 91/04165) where additional friction, spring and connecting elements are provided to produce the friction.
An arrangement is known from the German Patent Application DE 4 407 005 C1 where the friction is produced by pretensioning a friction mechanism through reset springs. A complicated large-scale transfer mechanism is used here and a radially displaceable wedge-shaped friction element is used to produce friction on a lever rigidly coupled to the pedal axis.
This arrangement requires several parts movable relative to each other and cannot be integrated in the pedal structure as a result of the large installation space required.
The present invention seeks to provide a pedal mechanism which transfers the pedal position simply and precisely to, for example, an electronic engine control unit whilst the driving feel remains unchanged compared to that of a conventional foot pedal connected via a Bowden cable.
According to the invention, there is provided a pedal mechanism comprising a pedal arm mounted on a base for rotation about a pivot axis, a cylinder fixed to the arm and open at one end, a piston slideable inside the cylinder and projecting through the open end of the cylinder into frictional contact with a surface of the base and means for biasing the piston in a direction towards the open end of the cylinder, the position of the piston and cylinder relative to the pivot axis being such that as the pedal arm rotates about the pivot axis, the piston is moved either into the cylinder by pressure between the piston and the surface of the base or out of the cylinder by the biasing means, to provide a resistance to rotational movement of the pedal in one rotational direction, and a restoring force assisting rotational movement of the pedal in the other rotational direction.
The pedal mechanism can be used in a motor vehicle. When the pedal arm is depressed by a driver""s foot, the angular movement of the pedal arm will cause the point where the piston makes contact with the base to move relative to the base, producing a frictional force that can be felt by the driver.
The mechanism preferably includes a position sensor for sensing the angular position of the pedal arm and for sending a position signal to an engine management system controlling the power output of the vehicle engine.
In a preferred embodiment, the position where the piston makes contact with the surface of the base is enclosed within the base. The base can be a substantially enclosed housing with an opening through which the pedal arm projects into the housing. The pivot axis is preferably contained within the housing. Surfaces on the arm and adjacent surfaces of the housing can combine to form a labyrinth seal which allows relative movement between the arm and the base but hinders the ingress of foreign matter into the housing. These surfaces which combine to form a labyrinth seal can also form stops to limit pivoting movement of the arm relative to the base.
Preferably, the cylinder will be formed integrally with the pedal arm. The pedal arm can be moulded of plastics material and the cylinder can be formed as part of the moulding. The base may also be formed from moulded plastics material.
The pedal mechanism with the position sensor can be arranged such that the pedal is urged by the biasing means towards the end of its travel corresponding to the idle position, so that when the driver""s foot is released from the pedal, the pedal returns to the idle position.
The piston preferably has a friction modifying surface where it makes contact with the base, and/or the base has a friction modifying surface where it makes contact with the piston.
The biasing means will preferably comprise at least one helical compression spring compressed between the base of the cylinder and the piston. Preferably, the biasing means will comprise two helical springs of different diameters with one spring fitted inside the other.
One end of the biasing springs will preferably be located within an annular groove formed in the base of the cylinder. The other end of the springs may be located in an annular groove formed in the piston.
The end of the piston in contact with the base will preferably be rounded, so as to reduce the dependence of the contact area on the angular position of the foot pedal and to improve the uniformity of the friction. The area of the base in contact with the piston will preferably be substantially flat, normal to the plane of movement of the foot pedal. The end of the piston may be rounded so that it is rotationally symmetric about the piston axis, or may be curved in only one plane, so that the piston end is in line contact, rather than point contact, with the surface of the base.
The base may comprise a substantially enclosed housing having a first face adapted to be mounted on the floor of a motor vehicle and a second face substantially opposite to the first face. The housing also has substantially continuous surfaces connecting the first and second faces, with an opening through which the pedal enters the housing being only large enough to just permit the full range of pedal movement relative to the housing. Preferably the surface of the base with which the cylinder is in contact is on the internal side of the second face, such that the contact surfaces are remote from the floor of the vehicle. In this way, the possibility of dust ingress or fouling by applied oil sprays or the like is minimized.
End stops for pedal arm movement may be mounted on the base, the end stops cooperating with a part of the pedal arm which lies on the opposite side of the pedal arm axis to the foot pad. The end stops may be formed with an elastic noise-damping material.
Alternatively, the end stops may lie on the same side of the pedal arm axis as the foot pad, and may form a labyrinthine passage from the exterior of the housing to the interior, to reduce the possibility of foreign matter entering the housing.
The pedal position sensor can be mounted on the base and can be mounted to enable it to be rotated to set an accurate rest position.
Preferably, the cylinder will be arranged on the pedal arm such that the direction of relative movement of the piston within the cylinder is substantially tangential to an arc of travel of the pedal arm. However, the cylinder may be arranged such that the piston is oriented on the pedal arm to within 60 degrees of the tangential direction.
The pedal mechanism may be specifically adapted to function as an accelerator or a brake pedal mechanism, for a motor vehicle. If the pedal and the housing/base are moulded from plastics material the mechanism can be very light in weight, in comparison with prior art mechanisms which are generally made (at least in part) in metal.
It may be desirable to provide a xe2x80x98kick-downxe2x80x99 function in which, towards the end of pedal travel, there is a substantially increased resistance to further pedal movement which can be overcome by substantially increased pressure from the driver""s foot.
To achieve this functionality, the end of the cylinder which makes contact with the base may meet a step on the base, and the cylinder is able to ride over this step, but only on application of a substantially greater force. In a further improvement, the cylinder may carry, near its end in contact with the base, a roller which is free to roll relative to the cylinder about an axis parallel to the pivot axis of the pedal, with this roller being out of contact with the base surface during normal angular movement, but making contact with, and riding over the step, at the end of travel to provided an increased pedal resistance to the last part of the pedal travel.
It will be understood that the piston and cylinder need not be of circular cross section, and may for example be generally rectangular in cross section.
The invention also provides a pedal mechanism comprising a pedal arm mounted on a base for rotation about a pivot axis, a friction surface on the base and a friction surface mounted on the pedal arm, the friction surfaces being arranged so that they move over one another as the pedal arm pivots about its pivot axis to provide a resistance to pivoting movement in one direction and a restoring force assisting pedal movement in an opposite direction, wherein the friction surfaces are biased against one another by a spring mounted on the arm.